Optical waveguides are used for transporting a variety of signals such as voice, video, data transmission, and the like along an optical communication network. The optical communication network has power losses that must be budgeted for when designing the network. By way of example, power losses include losses in the optical waveguide and insertion losses from connectivity points such as optical fiber jumper cables. A system designer must be concerned with these power losses when designing an optical network because the transmitting/receiving equipment must have a signal with enough power to overcome the power losses and maintain signal recognition.
In the optical communication industry it is desirable to test the performance of optical fiber jumper cables for parameters such as an optical insertion loss so the power loss is known. Typically, the optical performance of each optical fiber jumper cable (hereinafter jumper cable) is tested before the leaving the factory. Thus, the optical power losses due to the jumper cable can be accounted for when designing the optical network.
With the increasing use of low-power optical transmitting/receiving devices, minimizing the insertion losses at connection points is becoming more important. To support these low-loss optical systems, the industry is developing low-loss components such as low-loss optical connectors. However, low-loss components must be tested to ensure that they meet the required low-loss specifications. For instance, high-performance connectors on jumper cables should have a mated pair insertion loss under 0.1 dB.
Conventional testing of jumper cables requires physically mating the connector ferrules of the jumper cable being tested with a low-loss reference jumper cable and an optical power meter. For instance as shown in FIG. 1a, a benchmark insertion loss measurement of a reference jumper cable 10 is made by connecting the same across the optical power meter 5 to determine the insertion loss of reference jumper cable 10. Thereafter, an end 10a of reference jumper cable 10 is disconnected from an input connection 5a of optical power meter 5. Then as shown in FIG. 1b, a first optical connector (not visible) on first end 14a of a jumper cable 14 being tested is mated with an optical connector of reference jumper cable 10 disconnected from input connector 5a of optical power meter 5. A second optical connector (not visible) on second end 14b of jumper cable 14 being tested is connected to input connector 5a of optical power meter 5 and the optical power loss is measured. The difference between this measured insertion loss and the benchmark insertion loss is calculated, thereby yielding an insertion loss for jumper cable 14. In other words, the insertion loss measured for reference jumper cable 10 is subtracted from the insertion loss of the connected reference and tested jumper cables 10,14 to calculate the insertion loss of jumper cable 14.
This method of measuring the insertion loss of a jumper cable has several disadvantages. First, the conventional apparatus and method is a contact process. Stated another way, the optical connection portion of the connector ferrule of the jumper cable being tested must contact the respective surface of the reference jumper cable. This contact process can have the drawbacks of leaving permanent marks on the polished ferrule/optical fiber end face of the connector (hereinafter ferrule end face), transferring contaminant to the ferrule end face, and/or relatively large measurement variability.
Leaving permanent marks on the ferrule end face is undesirable because end users generally find permanent marks unacceptable when they are numerous, large, and/or close to the optical fiber. Transferring contaminants can cause erroneous readings and requires cleaning of the equipment and ferrules then taking another measurement, which is time-consuming and inconvenient. The measurement variability of the conventional testing method is relatively large compared with the limitation of 0.1 dB insertion loss for high-performance jumper cables. Thus, high-performance jumper cables that meet the 0.1 dB insertion loss specification may be wrongly accepted or unnecessarily rejected because of measurement variability. Furthermore, the connecting and disconnecting of the reference jumper cable during the contact process eventually cause wear on the ferrule end faces and the reference jumper cable must be replaced. Replacing the reference jumper cable can bias the measurement process in an unpredictable manner, plus maintaining and replacing the same is time-consuming and expensive.